This disclosure directs itself to a variable tone configuration control for string instruments that permits switching between series and parallel configurations of pairs of electromagnetic pick-up coils and intermediate variations thereof. More in particular, the disclosure is directed to a variable tone configuration control for string instruments that includes a pair of pickup coils disposed on a string instrument for inducing voltages therein responsive to vibration of at least one string of the string instrument and the pair of potentiometers are coupled to a pair of output terminals and the displaceable contact of each of the potentiometers is electrically connected to a respective one of the pair of pickup coils for selective operative coupling of the pair of pickup coils coupled in series to the output terminals, or the pair of pickup coils coupled in parallel to the output terminals, responsive to a position of displaceable contacts of the pair of potentiometers. Still further, the disclosure is directed to a system wherein the selective operative coupling between the pair of pickup coils and the output terminals that is provided by the pair of potentiometers additionally selectively provides the effective coupling of only one of the pair of pickup coils to the output terminals. Further, the system can provide selective operative coupling of one of said pair of pickup coils in combination with a series coupling of the pair of pickup coils, or can provide selective operative coupling of a the pair of pickup coils where the output provides contributions from both series and parallel coupling of the pair of pickup coils.
Electric string instruments, such as electric guitars, electric bases, electric violins, etc., use a pickup to convert the vibration of instrument's strings into electrical impulses. The most commonly used pickups uses the principle of direct electromagnetic induction. The signal generated by the pickup is of insufficient strength to directly drive an audio transducer, such as a loudspeaker, so it must be amplified prior to being input to the audio transducer.
Because of their natural inductive qualities, all magnetic pickups tend to pick up ambient electromagnetic interference (EMI) from electrical power wiring in the vicinity, such as the wiring in a building. The EMI from a 50 or 60 Hz power system can result in a noticeable “hum” in the amplified audio by from the audio transducer, particularly with poorly shielded single-coil pickups. Double-coil “Humbucker” pickups were invented as a way to overcoming the problem of unwanted ambient hum sounds. Humbucker pickups have two coils arranged to be of opposite magnetic and electric polarity so as to produce a differential signal. As ambient electromagnetic noise effects both coils equally and since they are poled oppositely, the noise signals induced in the two coils cancels out. The two coils of a Humbucker are often wired in series to give a fuller and stronger sound.
While most single coil pickups are wired in parallel with each other, it is also possible to wire them in series, producing a fuller and stronger sound. The two coils of a Humbucker type pickup can be connected in parallel. This results in a brighter sound, but at the cost of a lower output as with a single-coil pickup, but with the pickup's hum-cancelling properties still being retained. Using a multiple pole, multiple through switch, such as a double pole, double through switch (DPDT) or double pole three position switch, it is known in the art to switch the coil configuration between series and parallel, and may also provide or “coil cut” configuration (a single coil output).
Blend potentiometers, usually formed by two potentiometers ganged together to be rotated by a single shaft, allow blending together outputs of two pickup coils in varying degrees, not unlike a balance control provided in stereo equipment. Blend potentiometers, however, do not accomplish switching of the coil configuration. In one known prior art system disclosed in U.S. Pat. No. 4,423,654, a tone control formed with a pair of ganged rheostats is connected to the two coils of a Humbucker type pickup. The operation of this tone control provides a series coil configuration at one end of the rotation of the control and a parallel configuration at the opposing end of the rotation thereof. Of the two rheostats used, the resistance element of one is configured to have substantially zero resistance (zero ohms) between one end terminal and the midpoint of the resistance element's length and thereafter increase linearly, while the other rheostat has a resistance that increases logarithmically along its length. Due to the logarithmic taper of the resistance element, from the one end of the travel of the control that provides a series configuration of the coils to and including the midpoint thereof, the series configuration is maintained, changing only the high frequency attenuation included in the control.